T. Wakui

Analyzing power in elastic scattering of 6He from a polarized proton target at 71 MeV/nucleon

The vector analyzing power has been measured for the elastic scattering of neutron-rich {sup 6}He from polarized protons at 71 MeV/nucleon making use of a newly constructed solid polarized proton target operated in a low magnetic field and at high temperature. Two approaches based on local one-body potentials were applied to investigate the spin-orbit interaction between a proton and a {sup 6}He nucleus. An optical model analysis revealed that the spin-orbit potential for {sup 6}He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semimicroscopic analysis with an {alpha}+n+n cluster folding model suggests that the interaction between a proton and the {alpha} core is essentially important in describing the p+{sup 6}He elastic scattering. The data are also compared with fully microscopic analyses using nonlocal optical potentials based on nucleon-nucleon g matrices.

Analyzing power for proton elastic scattering from the neutron-rich He6 nucleus

Vector analyzing power for the proton-{sup 6}He elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target, which works at a low magnetic field of 0.09 T. The results are found to be incompatible with a t-matrix folding model prediction. Comparisons of the data with g-matrix folding analyses clearly show that the vector analyzing power is sensitive to the nuclear structure model used in the reaction analysis. The {alpha}-core distribution in {sup 6}He is suggested to be a possible key for understanding the nuclear structure sensitivity.

Studies of Unstable Nuclei with Spin-Polarized Proton Target

Roles of spin-dependent interactions in unstable nuclei have been investigated via the direct reaction of radioactive ions with a solid spin-polarized proton target. The target has a unique advantage of a high polarization of 20–30% under low magnetic field of 0.1 T and at a high temperature of 100 K, which allow us to detect recoil protons with good angular resolution. Present status of on-going experimental studies at intermediate energies, such as proton elastic scattering and (p, 2p) knockout reaction, and new physics opportunities expected with low-energy RI beams are overviewed.

PULSE STRUCTURE DEPENDENCE OF THE PROTON SPIN POLARIZATION RATE

The proton polarization is obtained at high temperature and in low magnetic field by means of photo-excited triplet state of aromatic molecules. For this method, we use a continuous wave Ar-ion laser which is pulsed by an optical chopper. In this system, the photon number is the bottleneck in achieving higher polarization. The proton polarization rate was measured by changing a duty from 5 % to 50 % and a reputation frequency from 0.75 kHz to 10.6 kHz. For a duty factor of 50 % and a repetition frequency of 10.6 kHz, the polarization rate can be a factor five larger than that for the old setting.

Elastic Scattering of Neutron-Rich Helium Isotopes from Polarized Protons at 71 MeV/A

The vector analyzing power has been measured for the elastic scattering of neutron-rich 6He and 8He from polarized protons at 71 MeV/A making use of a newly constructed solid polarized proton target operated in a low magnetic field of 0.1 T and at a relatively high temperature of 100 K. An optical model analysis revealed that the spin-orbit potentials for 6He and 8He are characterized by shallow and long-ranged shape compared with the global systematics of stable nuclei. Such a characteristics reflect a diffused density distribution of the neutron-rich isotopes.

Half-life and magnetic moment of the first excited state in {sup 132}I

The half-life and the magnetic moment were measured for the first excited state in {sup 132}I, of which the inconsistent results on the half-life have been reported by several other groups. This time, measurements were performed on {sup 132}I obtained as a decay product of a {sup 132}Te radioactive beam from the ion guide at Tohoku University. The half-life of this level was determined to be T{sub 1/2}=1.120{+-}0.015 ns using a conventional coincidence technique with a pair of BaF{sub 2} detectors. The time-differential perturbed angular correlation technique was successfully applied to the first excited state in {sup 132}I implanted into nickel foils. The magnetic moment of this state was determined to be {mu}=+(2.06{+-}0.18){mu}{sub N}. The present results are consistent with values reported by Gorodetzky et al. and Singh et al.

Analyzing Power Measurement for Elastic Scattering of 6He on Polarized Protons

Vector analyzing power was measured for the proton elastic scattering on 6He at 71 MeV/u. We applied a solid polarized proton target, which was operated in a low magnetic field of 88 mT and at high temperature of 100 K, to a radioactive‐isotope beam experiment. Low energy recoil protons were successfully detected due to the modest operation conditions of the target. Selection of p+6He elastic scattering events was clearly carried out with detected protons. Absolute values of the analyzing power were determined for the first time.

Spin correlation parameter C{sub yy} of p+{sup 3}He elastic backward scattering

We measured the differential cross section and the spin correlation parameter C{sub yy} of the p-vector+{sup 3}He-vector elastic backward scattering at 200, 300, and 400 MeV at {theta}=180 deg. in the center-of-mass frame to study the mechanism of the reaction and to examine the validity of the {sup 3}He wave functions based on two different realistic two-body forces. This is the first measurement of the spin correlation parameter C{sub yy} of the p-vector+{sup 3}He-vector EBS at intermediate energies. The experimental results were compared with few-body calculations, including three reaction mechanisms: two-nucleon-pair exchange, pion exchange, and direct pp scattering. It was found that few-body calculations describe the differential cross-section data reasonably well. The spin correlation parameter C{sub yy} shows clear evidence for the two-nucleon-pair exchange processes in the reaction, demonstrating that the spin observables are helpful for deeper understanding of the reaction mechanism.

Development of a polarized proton target in a low magnetic field at high temperature

A proton polarizing system have been designed and constructed in order to develop a polarized proton solid target applicable to an experiment with a radioactive isotope beam. Protons are polarized by a method called microwave-induced optical nuclear polarization. Our goal is to attain a polarization of more than 30% in the target sample with a diameter of 20 mm and a length of 5 mm.